The proliferative activity of gastric cancer cells was determined by DNA flow cytometric (FCM) analysis and labeling rates of Ki-67 and monoclonal antibodies and proliferation-associated nuclear antigen (p105) autoantibodies in 28 patients with fresh human gastric cancer cells. By setting the cutoff line at the level as used in a negative control study without primary antibody in the same sample, the Ki-67 and p105 labeling rates were calculated by the dual fluorescence analysis. A total of 43 experiments was performed on FCM analysis for each antigen: 28 with Ki-67 and 15 with p105. The mean Ki-67 labeling rate of gastric cancer cells was 45.1% (13.9-76.3%). The Ki-67 labeling rates were significantly higher for larger size tumor, peritoneal metastasis, and advanced clinical stage. A significant correlation was found between Ki-67 labeling rate and p105 labeling rate (P < 0.05). Bivariate FCM may be an easy method for obtaining useful information of cell kinetics.